WO 00/37225 describes a hair cutting apparatus including a cutter head mounted on a housing of the apparatus for pivotal motion about an axis. A cutting comb of the cutter head has two associated cutting blades that are adapted to be coupled to a drive element of a drive mechanism. Each of the cutting blades is dependent upon the pivot position of the cutter head. One of the cutting blades is generally disengaged so that only one cutter unit is driven at a time. The axis about which the cutter head is pivotal extends parallel to the cutting edges of the cutting combs or cutting blades. The cutter head is carried at either end in a fork-shaped socket in the housing of the hair cutting apparatus. The pivot axis extends centrally relative to the two cutting elements. Coupling elements are connected to cutting elements of the cutting blades. The coupling elements, for engagement with an eccentric drive, include sloping enlargements to facilitate introduction of the eccentric device in various operating positions. It is necessary to turn off the drive before pivoting the cutter units.
US 2003/0106219 A1 describes another hair cutting apparatus that has a pivotal cutter head with two cutter units, a narrower one and a wider one. The two ends of the cutter head are carried in a casing, with the pivot axis extending normal to a plane formed by the two cutter units. The pivot axis extends centrally relative to the two cutting elements. In order to enable the cutter head to be rotated relative to the casing with the motor turned on, a coupling device is provided. The coupling device temporarily interrupts the driving relationship between motor and shaving unit.